Hydraulic apparatus

ABSTRACT

A hydraulic displacement device such as an internal gear pump having an internally toothed gear in mesh with an externally toothed gear, a high pressure zone and a low pressure zone defined within the internally toothed gear and separated by the meshing position of the gears and an end bearing member loaded by liquid at the pressure of the high pressure zone to engage the end surfaces of the gears. In order to reduce excessive friction between the end bearing member and the gears the bearing member has an area of engagement with an end surface of the gears in the vicinity of the high pressure zone with part of its boundary at a position intermediate the tooth root radius and the periphery of the internally toothed gear.

United States Patent 1 Lambeth [54] HYDRAULIC APPARATUS [75] Inventor:Dennis Ernest Lambeth, Benhall,

Cheltenham, England [73] Assignee: Dowty Technical Developments Limited,Cheltenham, England [22] Filed: Mar. 22, 1971 [21] Appl. No.: 126,553

UNITED STATES PATENTS 3,496,877 2/1970 Eckerle et a1. ..4l8/13l2,405,061 7/1946 Shaw ..418/l32 1,802,527 4/1931 Nichols ..4l8/1693,204,564 9/1965 Elitze ..4l8/l70 2,808,785 10/1957 Hilton "418/1323,303,793 2/1967 Morita ..4l8/132 1 May 1, 1973 2,855,854 lO/l958Aspelin .418/126 Primary ExaminerCarlton R. Croyle AssistantExaminer-John J. Vrablik Attorney Young & Thompson [57] ABSTRACT Ahydraulic displacement device such as an internal gear pump having aninternally toothed gear in mesh with an externally toothed gear, a highpressure zone and a low pressure zone defined within the internallytoothed gear and separated by the meshing position of the gears and anend bearing member loaded by liquid at the pressure of the high pressurezone to engage the end surfaces of the gears. In order to reduceexcessive friction between the end bearing member and the gears thebearing member has an area of engagement with an end surface of thegears in the vicinity of the high pressure zone with part of itsboundary at a position intermediate the tooth root radius and theperiphery of the internally toothed gear.

2 Claims, 4 Drawing Figures Patented May 1, 1973 3,730,656

2 Sheets-Sheet 1 INVENTOR 0.6mm: fen/3 7' La M15577;

BY (4M7, r L, /5544 [ATTORNEYS Patented May 1, 1973 1 3,130,656

2 Sheets-Sheet 2 INVENTOR fii/wv/s fen/asrla/vaz/v %:I7 YUM ATTORNEYSHYDRAULIC APPARATUS This invention relates to a hydraulic displacementdevice having an internally-toothed gear in mesh with anexternally-toothed gear, a high-pressure zone and a low-pressure zonedefined within the internally toothed gear and separated by the meshingposition of the gears, a high pressure connection for the high-pressurezone and a low pressure connection for the low-pressure zone and atleast one end bearing member being loaded by liquid at the pressure ofthe high pressure zone to engage end surfaces of the gears. Thiskind ofhydraulic displacement device will hereinafter be referred to as apressure loaded internal gear device.

Where a pressure loaded internal gear device is provided for operationat high pressure the internallytoothed gear must be of substantialradial thickness in order to provide adequate strength to resist theaction of pressure in the high pressure zone which will tend to distortthe internally-toothed gear out of its circular form.

The present invention has for its object to provide an improved form ofpressure loaded internal gear device for reliable and efficientoperation at high pressures.

in accordance with the present invention, a pressure loaded internalgear device comprises a casing, an internally toothed gearand anexternally toothed gear both rotatably mounted within the casing withteeth in mesh, the externally toothed gear being supported by a pair ofshafts extending c-axially from the ends thereof into bearings withinthe casing, an end bearing member mounted within the casing for axialfloating movement to enable a flat bearing surface thereof to engage theflat ends of the gears adjacent to one shaft, a load reacting memberforming part of the casing having a flat reacting surface adjacent to aflat loading surface formed on the bearing member opposite to thebearing surface, sealing means located between the loading surface andthe reacting surface to define a balancing zone, a passage connectinghigh pressure liquid from the high pressure zone between the gears tothe balancing zone whereby the end bearing member is urged against theend surfaces of the gears to seal the high pressure zone within thegears, a groove in the bearing surface of the end bearing memberconnecting the low pressure zone between the gears to some of theintertooth spaces of the gear teeth not in mesh with one another, thearea of engagement between the flat bearing surface of the end bearingmember and the flat end surfaces of the gears in the neighborhood of thehigh pressure zone terminating between the tooth root radius and theperiphery of the internally toothed gear.

Where a land is located in between the gears having curved surfaces toengage the gear tooth tips at nonmeshing positions thereof, the lowpressure zone may be connected to some of the inter-tooth spaces ofteeth not in mesh with one another be means of a groove in the surfaceof the land.

One embodiment of the invention for use as a pump will now beparticularly described with reference to the accompanying drawings, inwhich,

FIGS. 1 and 2 are longitudinal cross-sections lying at right angles toone another through the pump,

FIG. 3 is a cross-section on the line Ill-III in FIG. 1, and

FIG. 4 is a cross-section on the line IV--IV in FIG. 1.

The pump casing comprises an annular member 1 in ternally bored toreceive a thin plain metal bearing 2 having an internal cylindricalbearing surface 3. A pair of end covers 4 and 5 are secured to theannular member 1 by a plurality of bolts 6. The end covers 4 and 5 areprovided respectively with extensions coaxially known in parallel to theaxis of the member 1 but eccentric relative thereto the bores beingprovided with cylindrical bearing sleeves 7 and 8. The bearing sleeves 7and 8 carry two parts 9 and 11 ofa hollow drive shaft which areintegrally formed with an externally-toothed driving gear 12. Thedriving gear 1.2 meshes with an internally-toothed gear ring 14 whosecylindrical external surface 10 fits closely within the bearing surface3 for rotation therein. The teeth 15 of the gear 12 and the teeth 16 ofthe gear ring 14 are accurately shaped in a .manner well known instandard gear technology to minimize sliding contact between the gearteeth. The radial thickness of the gear ring 14' from the tooth roots tothe outer periphery is quite substantial having regard to the highoperating pressure intended for the pump.

The eccentric location of the gear 12 relative to the gear 14 is suchthat at one position, indicated at 17 in FIG. 4, the teeth 15 and 16 arein full mesh. A crescentshaped space exists between the paths swept bythe teeth 15 and 16, the space being occupied by a crescent-shaped land18 which has a pair of part cylindrical surfaces 19 and 21 which arespaced with a very small clearance from the tips of the teeth 15 and 16respectively in the crescent-shaped space to provide effectivelyfluid-tight engagement between the surfaces 19 and 21 and the tips ofthe teeth. The land 18 is firmly secured in position as will bedescribed further in this specification.

The end surfaces of the two gears 12 and 14 are accurately finishedplane surfaces the axial length of the two gears measured between theend surfaces being exactly the same. A thin sheet metal bearing member22 is secured to the inner surface of the end cover 5 to engage one pairof end faces of the gears. The sheet metal bearing member 23 is mountedon the internal surface of the end cover 4 with the ability to move asmall degree in the axial direction. The land 18 is secured by bolts 24to the end cover 5, such bolts passing through the bearing member 22into the land 18, the tension in the bolts tightly gripping the. bearingmember 22 between the land 18 and the end cover 5. Accurate locationforthe land 18 is ensured by dowel pins 20 (see FIG. 4).

A pair of ports 25 and 26 (see FIG. 2) are formed through the bearingmember 22 and co-operate with the end faces of the gears, the port 25 inthe high pressure zone where the gears approach the fully meshedposition 17 and the port 26 in the low pressure zone where the gearsmove away from the fully meshed position 17. The port 25 is formed astwo holes through the bearing member 22, the portion of bearing memberbetween the holes forming a strengthening member against the action ofhigh pressure.

The end cover 5 on to which the bearing member 22 is attached is formedwith-inlet and delivery connections 28 and 29 (see FIG. 2) whichco-operate with the ports 26 and 25 in the bearing member 22respectively.

The port 31 is formed in bearing member 23 (see FIG. 2) at a'positioncorresponding to the inlet port 26 in the bearing member 22. The innersurface of end cover 4 (see FIG. 2) includes a recess 32 which feedsinlet liquid from the inlet port 28 to the port 31 through a pair ofpassages 33 in the member 1. A recess 30 similar to recess 32 is alsoformed in the end cover to extend from the inlet connection 28 to thepassages 33. A hole 34 in the bearing member 23 is shaped so as to fitaround an extension 35 on the end of the crescent land 18. The extension35 is so arranged as to leave a shoulder 36 around the crescent-shapedland. The length of the land measured in the direction of the rotationaxis from shoulder 36 to bearing member 22 is as accurately as possiblethe same as the axial length of the gears between their end surfaces.

A pair of bolts 38 extend through the end cover 4 and the extension 35into the land and during assembly of the pump the two sets of bolts 38and 24 are tightly screwed into position to help the two end covers 4and 5 to resist any outward forces generated by hydraulic liquid in thepump.

In order to provide pressure loading on the bearing member 23 acontinuous groove 39 (see FIGS. 2 and 3) is formed on the inner surfaceof the end cover 4. A rubber seal 41 (FIG. 2) fits into the groove 39and engages against the bearing member 23 to define a loading zone 40 onthe side of the bearing member 23 opposite to the high pressure zone inbetween the gear teeth and 16 as they are coming to the full meshingpoint 17 during rotation. Liquid at pressure is fed through hole 42 inbearing member 23 from the high pressure zone.

Both bearing members 22 and 23 are circular in form and theirperipheries respectively 44 and 45, engage the end surfaces of the gearring 14 at positions intermediate the tooth root radius and thecylindrical bearing surface 3. This arrangement ensures that the highpressure zone between the meshing teeth 15 and 16 is sealed againstoutward leakage but at the same time ensures that the area of contactbetween the end surfaces of the gear ring 14 and the bearing members 22and 23 is kept to a reasonable minimum thus reducing frictional losses.The extension 35 has a thickness very slightly greater than thethickness of the bearing member 23 so that when the bolts 38 aretightened the bearing member 23 is still capable of very slight axialmovement. Rubber sealing rings 46 and 47 carried in grooves 48 and 49 inend covers 4 and 5 seal against the end surfaces of the annular member1.

When in use the gears as seen in FIG. 4 will rotate in a clockwisedirection the gear 12 being the driver gear. Liquid enters the pumpthrough connection 28 and through port 26 and 31 in the bearing members22 and 23 into the low pressure zone. Liquid fills the spaces betweenthe gears and as the gear teeth meet the curved surfaces 19 and 21 ofthe crescent land the spaces between the teeth will be sealed. As theteeth move into the high pressure zone towards the meshing position 17,the teeth 15 enter spaces between the teeth 16 and the teeth 16 enterthe spaces between the teeth 15 thus reducing the effective volume forliquid and creating pressure in the liquid. This pressure will react onthe teeth 16 to urge the gear ring 14 against the driving force exertedby the teeth 15. The teeth 15 and 16 at their meshing positions willseal one against the other to prevent the high pressure liquid frompassing the meshing point of the teeth towards the low pressure zone.The high pressure liquid is then urged out of port 25 into the deliveryconnection 29. Some of the liquid at pressure will pass through thesmall port 42 into the loading zone 40 defined by the seal 41. Thepressure in this zone will then react on the bearing member 23 to urgeit against the adjacent end surfaces of the gears 12 and 14 and at thesame time to urge the gears to the right as seen in FIGS. 2 and 3 sothat their opposite end surfaces engage the bearing surface 22. Thispressure loading ensures good sealing of the pressure zone between thegears 12 and 14 and helps to reduce leakage losses within the pump. Thepressure in the loading zone will also urge the bearing member 23against the shoulder 36 of the crescent-shaped land at that end of theland which helps to define the high pressure zone.

The described pump is suitable for operation at high speed and highpressure. Its ability to operate at high speed results from the factthat the relative rubbing speed between the teeth is extremely low dueto the fact that the gears are internally meshing. Its ability tooperate at high pressure results from the fact that the relativecurvatures of the engaging surfaces of the gears are such that the Hertzstress is low having regard to the pressure generated. For dealing withvery high pressures the two gears need to be made of very hard metalssuch for example as tool steel.

It is desirable to limit the high pressure zone between the gears tocontrol the magnitude and direction of the forces acting within thepump. For this purpose grooves are provided to connect some inter-toothspaces to the low pressure zone at positions where these inter-toothspaces are normally completely sealed. The groove may be provided as apair of grooves 53 and 54 in the surfaces 19 and 21 of thecrescent-shaped land extending from the low pressure end thereof andterminating short of the high pressure zone so that at least oneinter-tooth space maybe sealed adjacent to the high pressure zone. Thesegrooves may alternatively be provided as indicated at 55 in one or theotheror both bearing members 22 and 23.

Whilst the illustrated embodiment of pressureloaded internal gear deviceis intended for use as a pump it is equally possible within theinvention to provide a structure for use as a motor.

I claim:

1. A pressure loaded internal gear device comprising a casing, aninternally toothed gear and an externally toothed gear both rotatablymounted within the casing with teeth in mesh, the externally toothedgear being supported by a pair of shafts extending co-axially from theends thereof into bearings within the casing, an end bearing membermounted within the casing for axial floating movement to enable a flatbearing surface thereof to engage the flat ends of the gears adjacentone shaft, a load reacting member forming part of the casing having aflat reacting surface adjacent to a flat loading surface formed on thebearing member opposite to the bearing surface, sealing means locatedbetween the loading surface and the reacting surface to define abalancing zone, a passage connecting high pressure liquid from the highpressure zone between the gears to the balancing zone whereby the endbearing member is urged against the end surfaces of the gears to sealthe high pressure zone within the gears, a groove in the bearing surfaceof the end bearing member connecting the low pressure zone between thegears to some of the inter-tooth spaces of the gear teeth not in meshwith one another, the area of engagement between the flat bearingsurface of the end bearing member and the flat end surfaces of the gearsin the neighborhood of the high pressure zone terminating between thetooth root radius and the periphery of the internally toothed gear.

2. A pressure loaded internal gear device comprising a casing, aninternally toothed gear and an externally toothed gear both rotatablymounted within the casing with teeth in mesh, the externally toothedgear being supported by a pair of shafts extending co-axially from theends thereof into bearings within the casing, an end bearing membermounted within the casing for axial floating movement to enable a flatbearing surface thereof to engage the flat ends of the gears adjacentone shaft, a load reacting member forming part of the casing having aflat reacting surface adjacent to a flat loading surface formed on thebearing member opposite to the bearing surface, sealing means locatedbetween the loading surface and the reacting surface to define abalancing zone, a passage connecting high pressure liquid from the highpressure zone between the gears to the balancing zone whereby the endbearing member is urged against the end surfaces of the gears to sealthe high pressure zone within the gears, a land located in between thegears having curved surfaces to engage the gear tooth tips atnon-meshing positions of the gear teeth, securing means holding the landto the casing independently of the end bearing member, and a groove inthe surface of the land connecting the low pressure zone between thegears to some of the inter-tooth spaces of teeth not in mesh with oneanother, the area of engagement between the flat bearing surface of theend bearing, member and the flat end surfaces of the gears in theneighborhood of the high pressure zone terminating between the toothroot radius and the periphery of the internally toothed gear.

1. A pressure loaded internal gear device comprising a casing, aninternally toothed gear and an externally toothed gear both rotatablymounted within the casing with teeth in mesh, the externally toothedgear being supported by a pair of shafts extending co-axially from theends thereof into bearings within the casing, an end bearing membermounted within the casing for axial floating movement to enable a flatbearing surface thereof to engage the flat ends of the gears adjacentone shaft, a load reacting member forming part of the casing having aflat reacting surface adjacent to a flat loading surface formed on thebearing member opposite to the bearing surface, sealing means locatedbetween the loading surface and the reacting surface to define abalancing zone, a passage connecting high pressure liquid from the highpressure zone between the gears to the balancing zone whereby the endbearing member is urged against the end surfaces of the gears to sealthe high pressure zone within the gears, a groove in the bearing surfaceof the end bearing member connecting the low pressure zone between thegears to some of the inter-tooth spaces of the gear teeth not in meshwith one another, the area of engagement between the flat bearingsurface of the end bearing member and the flat end surfaces of the gearsin the neighborhood of the high pressure zone terminating between thetooth root radius and the periphery of the internally toothed gear.
 2. Apressure loaded internal gear device comprising a casing, an internallytoothed gear and an externally toothed gear both rotatably mountedwithin the casing with teeth in mesh, the externally toothed gear beingsupported by a pair of shafts extending co-axially from the ends thereofinto bearings within the casing, an end bearing member mounted withinthe casing for axial floating movement to enable a flat bearing surfacethereof to engage the flat ends of the gears adjacent one shaft, a loadreacting member forming part of the casing having a flat reactingsurface adjacent to a flat loading surface formed on the bearing memberopposite to the bearing surface, sealing means located between theloading surface and the reacting surface to define a balancing zone, apassage connecting high pressure liquid from the high pressure zonebetween the gears to the balancing zone whereby the end bearing memberis urged against the end surfaces of the gears to seal the high pressurezone within the gears, a land located in between the gears having curvedsurfaces to engage the gear tooth tips at non-meshing positions of thegear teeth, securing means holding the land to the casing independentlyof the end bearing member, and a groove in the surface of the landconnecting the low pressure zone between the gears to some of theinter-tooth spaces of teeth not in mesh with one another, the area ofengagement between the flat bearing surface of the end bearing memberand the flat end surfaces of the gears in the neighborhood of the highpressure zone terminating between the tooth root radius and theperiphery of the internally toothed gear.